Fluid-pressure device

ABSTRACT

A fluid-pressure device, operated as a pump, motor, or the like, and including cooperating inner and outer gear portions which are angularly movable in relation to one another, is caused to make tight line-contact sealing for entrapped fluid, by way of a plurality of pressure-actuated sealing rollers which exhibit only low levels of friction confined to limited sealing intervals during rotational cycles. In a fluid pump construction, based in part upon a known design in which the inner and outer gear portions have different numbers of teeth and in which the resulting tooth contacts function to prevent fluid leakage between spaced teeth, the outwardly projecting teeth of the inner gear portion are formed by cylindrical rollers radially pressurized into tight rolling line contact with surfaces of the surrounding internally toothed gear portion at selected intervals as the result of commutator-type valving of the fluid-pressures developed by the pump. Manufacturing tolerances are relatively noncritical, because of the dynamic operations of the roller teeth, and the outer gear portion, rollers, and pressure-applying inner gear support structure for the rollers, all possess axial symmetries which enable them to be manufactured conveniently and economically by separations from elongated extrusions, and the like.

United States Patent [72] lnventor Michel A. Plerrat Andover. Mass.

[21] Appl. No. 19.315

1221 Filed Mar. 13, 1970 {45] Patented Nov. 9, 1971 [73] Assignee Automatic Radio Mfg. Co.. Inc.

Melrose, Mass.

[54] FLUID-PRESSURE DEVICE 16 Claims, 8 Drawing Figs.

[52] US. Cl 417/440. 418/75.418/124.4l8/13l.418/171 [51] lnt.Cl FOlc 1/10. F03c 3/00. F04c 1/06 [50] Field of Search 418/82.

ABSTRACT: A fluid-pressure device. operated as a pump. motor. or the like. and including cooperating inner and outer gear portions which are angularly movable in relation to one another. is caused to make tight line-contact sealing for entrapped fluid. by way of a plurality of pressure-actuated sealing rollers which exhibit only low levels of friction confined to limited sealing intervals during rotational cycles. In a fluid pump construction. based in part upon a known design in which the inner and outer gear portions have different numbers of teeth and in which the resulting tooth contacts function to prevent fluid leakage between spaced teeth. the outwardly projecting teeth of the inner gear portion are formed by cylindrical rollers radially pressurized into tight rolling line contact with surfaces of the surrounding internally toothed gear portion at selected intervals as the result of commutatortype valving of the fluid-pressures developed by the pump. Manufacturing tolerances are relatively-noncritical. because of the dynamic operations of the roller teeth. and the outer gear portion. rollers. and pressure-applying inner gear support structure for the rollers. all possess axial symmetries which enable them to be manufactured conveniently and economically by separations from elongated extrusions. and the like.

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MICHEL A.,PIERRAT AT'TORN EY PATENTEDNUV 9 lSIl SHEET 3 BF 3 FIG.8

INVENTOR: M|CHELA.P|ERRAT FLUID-PRESSURE DEVICE BACKGROUND OF THE INVENTION The present invention relates to improvements in rotary apparatus of the type which operate on or are operated by fluids and which are uniquely rendered highly efficient in rugged low-cost constructions; in one particular aspect, a novel and improved refrigerant compressor or the like is tightly sealed internally by way of dynamically commutated fluid-pressurizing of rollers which effect low-friction sealing engagements between gear-type rotor and stator elements, whereby excellent sealing is efiected without severe power losses and without rapid deteriorations due to imperfect manufacturing tolerances, thermally induced dimensional changes, wear, and contaminations.

Fluid-pressure devices of the rotary type, including orbiting and eccentric elements, and including vanes, cooperating gear members, and the like, have of course been well-known in the art associated with pumping and with the production of motive power. In that class of devices utilizing radial vanes or pistons, the manufacturing and operating costs tend to be relatively high because of precisions needed to avoid internal leakages and because of power losses due to internal friction; moreover, such devices exhibit propensities toward serious vibration, are generally larger than desired for many applications, and wear rapidly. Gear-type devices, in which there are cooperating inner and outer elements having external and internal lobes or teeth, have promised theoretically attractive solutions to some of the problems associated with fluid pumps and motors, but, from a practical standpoint, very severe difficulties have been encountered. By way of example, such gear-type units have been known to involve an internally lobed outer member eccentrically meshed with an externally lobed inner member, the dimensions being carefully matched in effort to achieve fluid-tight sealing of certain fluid-filled regions between the members. Designs for the respective lobes are necessarily complex, and the matchings and mountings must be exact; even when these problems can be resolved at the price of high-attendant expense, the resulting sliding frictions necessarily induce severe wear and are responsible for wasteful power losses. In addition, the wear caused by fluid contaminants is not readily accommodated without impairing sealing, and, perhaps most importantly, thermally induced dimensional changes aggravate the difficulties inherent in such high-precision constructions.

SUMMARY OF THE INVENTION By way of a summary account of practice of this invention in one of its aspects, an improved fixed-displacement device such as a pump for a refrigerant (freon) includes cooperating inner and outer mated structures formed by relatively shortlength parts separated from elongated extrusions, the outer structure having axially extending surfaces contoured internally in a continuous sinuous fashion, and the eccentrically disposed inner structure having a plurality of dynamically actuated cylindrical rollers extending axially along its outer periphery at a number of positions which is one less than the odd number of sinuous undulations of the surrounding surfaces of the outer structure. Each of the rollers is partly recessed into a radially movable seat fitted into the inner structure as a piston, and ports in the latter structure admit fluid pressure below the seats to urge the associated rollers outwardly as commutated by high-pressure valving ports critically located in an end plate for the device. Fluid inlet and outlet ports are in communication with one another only by way of transport of volumes of the fluid through arcuate regions between the two structures, the highand low-pressure fluid ports of the device being separated at all times because of sealing effected by the rollers. Advantageously, only certain ones of diametrically opposite rollers need be pressurized at any instant, the remaining rollers being free of piston pressure and therefore avoiding deleterious frictions and power losses. Commutation of the valving occurs automatically as the inner structure rotates past valve ports in an end plate, the locations and spans of the latter ports being arranged to insure that the rollers at any instant disposed between the inlet and outlet port positions will be firmly pressurized into tight line-contact rolling-friction engagement with the surrounding surfaces. Valving pressures, taken from the high-pressure side of the device, increase automatically with demand and thus cause the tightness of internal sealing to increase only when necessary. Absence of differential pressures eliminates pressurizing of the rollers, and internal frictions can then be so low that in certain applications the device need not be mechanically disconnected, by costly accessory clutching or the like, to avoid serious wear problems such as may be encountered with other devices;

such differential pressures are readily dropped by selectably connecting the high-pressure and low-pressure sides of the device by way of a simple valve, such as solenoid-actuated valve built into the device.

Accordingly, it is one of the objects of the present invention to provide novel and improved fluid-pressure devices, such as pumps and motors, which are of economical manufacture and are caused to operate at high efficiency because of controlled pressurizing of sealing contacts.

Another object of the invention is the provision of a uniquely highly efficient fixed-displacement rotary fluid device of a gear type in which complex precision contouring of an externally lobed structure is avoided through use of pressure-actuated sealing rollers.

It is a further object to provide a compact fixed-displacement gear-type rotary fluid device of low-cost manufacture in which major components of devices of different capacity are severed in appropriate lengths from elongated stock, including components of pressure-actuated rolling seals.

Yet another object is the provision of gear-type rotary fluid devices in which internal fluid-tight sealing is achieved by simple rollers automatically pressureactuated into intermittent commutated line-contact rolling-type sealing actions.

Still further, an object of this invention is to provide unique, efficient, long-wearing fluid-pressure devices, such as rotary pumps and motors, in which rollers provide main internal seals only when selectably pressure actuated by internally developed fluid pressures, and in which adverse effects of friction, wear, and temperature-induced dimensional changes are minimized.

BRIEF DESCRIPTION OF THE DRAWINGS Although the features of this invention which are considered to be novel are set forth in the appended claims, further details as to preferred practices and as to the further objects and features thereof may be most readily comprehended through reference to the following description of preferred embodiments taken in connection with the accompanying drawings, wherein:

FIG. 1 is a partly cross-sectional side view of a pump embodiment of the improved fluid-pressure device;

FIG. 2 is a cross section of the same device taken along section line 2-2 in FIG. 1;

FIG. 3 pictorially represents the outer gear element of the device of FIGS. 1 and 2;

FIG. 4 illustrates the core of the inner rotor structure of the same device;

FIG. 5 depicts one of the cylindrical roller elements of the inner rotor structure of the same device;

FIG. 6 represents one of the pressure-actuated seat supports for a roller of the inner rotor structure of the same device;

FIG. 7 provides an end view of part of the housing of the device of FIGS. 1 and 2, exposing the relationship of fluid ports; and

FIG, 8 illustrates a portion of the housing of the same device, together with a solenoid-actuated bypass valving for controlling standby and operating conditions.

DESCRIPTION OF THE PREFERRED EMBODIMENT Having reference to the drawings, wherein the same reference characters designate identical or functionally corresponding parts throughout the several views, and, in the first instance specifically to FIGS. 1 and 2 thereof, there is designated a fixed displacement pump 11 for a fluid refrigerant, such as freon, which is appropriately actuated by a drive shaft 12 rotated by a suitable motive source (not shown). In a motor vehicle installation, for example, the required rotation of input shaft 12 may be by way of a pulley arrangement belting the relatively small device for drive by the engine, in tandem with the usual generator or alternator; flanges 13 on the housing [4 for the device provide for mounting after the fashion of such an alternator. As shown, housing 14 has a cylindrically surfaced cavity within which is disposed a closely mated generally annular outer gear element, 15, having seven generally sinuous undulations or lobes 16 (FIG. 2) about its inner periphery and a generally cylindrical outer periphery. In turn, the outer gear element is in surrounding relation to an inner rotor structure 17 keyed to shaft 12 for rotation by it, in the direction of arrows 18 in FIG. 2, for example. Structure 17 is a multipart arrangement of a rotor core 19 cooperating with six-cylindrical rollers, 20 through 25, each of the latter rollers being partly recessed into a channellike seat, all of which seats are alike and identified by the same reference character, 26. The seats and rollers are of the same axial length as the core 19, and the cylindrical outer surfaces of the rollers mate accurately with the associated inner cylindrical bearing surfaces disposed radially outwardly to receive the rollers and to permit their rotation about their longitudinal axes as the inner rotor structure turns. For the illustrated (FIG. 2) clockwise rotation of shaft 12 and rotor core 19, each of the rollers will tend to rotate counterclockwise in its seat, as designated by arrows such as arrow 27, although the entire array of rollers will of course be rotated clockwise at the same time.

For the assumed rotational conditions, one full clockwise revolution of the rotor structure 17 forces accompanying clockwise rotation (arrow 28) of the outer gear structure 15 within stationary housing 14, but the latter gear structure rotates less than one full turn, lessened by an amount equal to the full arcuate span of one of its lobes 16. This result obtains in a known way and in accord with known techniques, because of the intentionally preset eccentric displacement of the axis 2929 of drive shaft 12 in relation to the central longitudinal axis 30 (FIG. 2) of the outer gear element 15 and its housing.

In the embodiment which is under discussion for disclosure purposes, the spaces between the outer gear structure 15 and inner rotor structure 17 are filled with the fluid which is to be pumped from an inlet port through an outlet port associated with the housing, and provisions are therefore made to admit low-pressure fluid to certain of these spaces and to receive higher-pressure discharges of fluid from other of these spaces as the rotation progresses. Conveniently, the related porting is via one of the end sections, 140, of housing 14, so that the fluid is admitted and discharged laterally, and suitable locations for an inlet port 31 and outlet port 32 are displayed in FIG. 7. Automatic commutation or valving of pressurizings for the rollers 20-25 is also conveniently provided by way of two ports in the same end section, 14a, of housing 14, and the locus of a pair of such ports, 33 and 34, is also indicated by the linework on FIG. 7, to make clear the relationships between the flow ports and commutation ports. The commutation ports communicate the higher pressures of the fluid on the outlet side of the device, from the outlet port, to the undersides of roller seats 26 which have their associated pressure-transmitting channels, 35, aligned with these commutating ports at certain times. Seat openings 36 serve to communicate the fluid pressures from channels to the undersides of the rollers, thereby promoting the production of self-lubricating fluid films between the rollers and their mated bearing seats. Seats 26 have the dual function not only of mounting the rollers but, also, of forcing them radially outwardly into firm fluid-tight line-contact rolling engagements with the cooperating inner lobe surfaces of the outer gear structure 15, the latter surfaces being formed to extend axially so that the desired engagements and sealings will occur over the full axial lengths of the rollers and lobe surfaces. However, the said radially outward forcings occur strongly only when the undersides of certain, and not all, of the diametrically opposite seats are in communication with the commutation ports, such that frictional losses which could otherwise be associated with the remaining rollers are avoided. For purposes of the desired pumping, it is only necessary that the rollers seal those spaces in communication with the inlet port from those which are at the same time in communication with the outlet port, and the aforesaid dynamic pressurizings advantageously implement that purpose without involving heavy loadings and losses. What has been referred to above has to do with fluidtight sealings in the radial directions, and it is evident that these must also be complemented by sealing at the axial extremities of the two rotatable structures, if the device is to operate properly. Such end sealings are provided by abutting the axial extremities of the rotatable structures with substantially flat or planar bearing surfaces at all places except where the aforesaid ports appear. Preferably, these bearing surfaces are formed by plates 37 and 38 of high-lubricity material such as a polytetrafluoride plastic, although in some instances these may be dispensed with in favor of an alternative such as that involving a suitably coated metal. The portions of the ports through the end hearing 37 are appropriately aligned with those in the housing end section 140, of course. End sealing, like radial sealing, preferably should be made tighter when the pumping demands increase, and may be released when the device is idling. Accordingly, it is advantageous to utilize a pressure-responsive end plate 39 which forces the end bearing more firmly against the gear structures when the outlet pressure increases. In this connection, the pressure plate 39 is slidable somewhat within housing 14, and is equipped with O-ring seals 39a and 39b, in the cavity between which the high-outlet pressure is normally communicated by way of suitable channelling (not visible in the illustrations) from the high-pressure port of the device, to force the plate inwardly. Only relatively low pressure normally exists in the cavity 41 between the housing end cap 14b and the pressure plate, such that the pressure plate responds to the high pressures in the said cavity 40, as intended.

The aforesaid arrangement of movable parts may be economically fabricated from equal length sections taken from elongated stock, such as extrusions which may be readily produced in the desired cross-sectional configurations. Subsequent finishings, where needed, may then be accomplished with relative ease. In FIG. 3, for example, the outer gear element is, with its interior lobe surfaces 16, may be of any desired length, related to capacity of the device in which it is to be used, as the result of being severed from a longer unit, characterized by the dashed linework 42. Similarly, the core 18 of the rotor structure may be taken from an elongated unit characterized by dashed linework 43 in FIG. 4. Rollers 20, in FIG. 5, are readily made available from cylindrical bar stock 44, or from lighter weight hollow tubular stock. And, pressure seats 26, in FIG. 6, are likewise conveniently removed in sections from the proper form of channel-type stock 45. Because of the relatively important end-sealing requirements, each of the parts of the outer gear and rotor assembly should be of substantially the same axial length, and this may be assured by the simple expedient of lapping the assembled parts, as a unit, before they are inserted into the housing which is to receive them. For the different capacities desired, a wide variety is obtainable from given stock by selecting the axial lengths appropriately. Unlike those of other gear-type devices, the inner rotor structures are not of particularly complex outer-surface configurations, and manufacturing tolerances are not as troublesome as might ordinarily be expected, inasmuch as the pressurized rollers automatically accommodate certain dimensional variations. The numbers of gear lobes and cooperating rollers selected in the case of the illustrated embodiment may be altered in other designs, obviously.

The arrangement of ports appearing in FIG. 7 is one which is appropriate to lie behind the gear and rotor structures as depicted in FIG. 2. As the rotor shaft 12 is driven clockwise, fluid enters the left-hand spaces laterally between the two structures (FIG. 2) from the inlet port 31 via a housing inlet connection 46, and is angularly conveyed between rollers, such as adjacent rollers 25 and 20, past the inlet port and over to the outlet port 32, whence it egresses at higher pressure via the housing outlet connection 47. Throughout the rotation of the rotor structure, the larger spaces and fluid volumes between adjacent rollers appear at the top (in the FIG. 2 illustration), due to accompanying slightly lesser rotation of gear element 15, and these successive volumes are brought around to the outlet port, provided the sealing between adjacent rollers there and at the diametrically opposite position between the two angularly separated ports is maintained relatively tight. The latter sealings are very effectively and efficiently promoted by the automatic pressurizings of the rollers at these two diametrically opposite sites as the spaces 35 below their slightly movable seats 26 come into communication with the commutation or valving ports 33 and 34. The commutating ports are angularly located generally at the sites between the fluid ports, and are at a different radial distance, inwardly, such that the seats are pressurized only as dictated by the commutating ports. Relatively high-fluid pressures, for actuations of the roller seats, are preferably taken from the outlet side, and dashed-line channel 48 in the housing establishes such a coupling of high-fluid pressures with the commutation ports. These pressures vary automatically with the demands on the device, and therefore desirably cause the tightness of sealing to improve with demand. Only the diametrically opposed rollers at the sites of the commutation ports are pressurized at any instant, and the rollers between them are relatively loose, such that total friction is minimized. Friction is inherently low in any event, because of the rolling line-contact engagements made by the rollers, and because of the fluid-film lubrications created below the rollers in their seats.

The earlier-mentioned bypassing of the device, to relieve sealing pressures and reduce friction and losses during standby periods, is readily achieved through actuations of a solenoid valve unit 49, which appears in FIG. 8. There, a solenoid winding 50, when electrically energized during operation of the pump, lifts a balanced valve armature 51 against restraint ofa spring 52, and closes it against a valve seat 53 associated with an opening between the normally separated inlet and outlet supply channels in the housing; the fluid is then pumped. Absenting such electrical excitation, the valve armature is springopened to allow the fluid to bypass the pump, and both the aforementioned pressurizings of the rollers and of the pressure plate are advantageously relieved. Preferably, the solenoid valve unit takes the illustrated form of a cylindrical cartridge, including O-ring seals 54 and 55, which may be readily inserted and replaced, as a whole.

It should be understood that the specific practices and embodiments herein referred to have been offered by way of disclosure, rather than limitation, and that various modifications, additions and substitutions may be effected without departure from these teachings. In particular, it is to be noted that the device may find applications other than as a pump, such as that of a fluid-actuated motor. Seats for the rollers may be of high-lubricity plastic material, or may be eliminated where the rollers are properly fitted into accommodating rotor-core openings for them. Advantages of commutated, vs. continuous, pressurizings may also be realized when rollers are replaced by nonrotatable but radially pressurized rotor lobe elements. Both orbiting and nonorbiting type devices may exploit the concepts and teachings here submitted. Accordingly, it is aimed in the appended claims to embrace all such variations as fall within the true spirit and scope of this invention.

What I claim as new and desire to secure by Letters Patent ofthe United States is:

1. Apparatus of the type comprising a pair of cooperating rotor structures having external and internal lobes, respectively, one of said structures being mated eccentrically within and having one less lobe than the other, the lobes of said one of said structures being formed by rollers rotatably mounted on said one of said structures at angularly displaced positions and each disposed in substantially line-contact engaging relationship with lobe surfaces of the other of said structures, and means responsive to fluid pressures applying pressure to at least certain ones of said rollers at positions substantially opposite the positions of engagements thereof with said lobe surfaces of said other of said structures, whereby said rollers are pressurized into firm line-contact rolling engagements with said lobe surfaces of said other of said structures.

2. Fluid-pressure apparatus comprising a fluid-tight housing having a fluid inlet and outlet, a pair of cooperating rotor structures within said housing having external and internal lobes, respectively, one of said rotor structures being mated eccentrically within and having one less lobe than the other, the lobes of said one of said structures being formed by rollers rotatably mounted on said one of said structures at angularly displaced positions and each disposed in substantially linecontact engaging relationship with lobe surfaces of the other of said structures, port means connecting said inlet and outlet with spaces between said mated structures at different spaced angular positions, and means responsive to fluid pressures applying pressures to at least certain ones of said rollers at positions substantially opposite, the positions of engagements thereof with said lobe surfaces of said other of said structures, whereby said rollers are pressurized into firm line-contact rolling engagement with said lobe surfaces to effect tight sealing of said spaces.

3. Fluid-pressure apparatus as set forth in claim 2 wherein said one of said structures includes a core on which said rollers are carried about the outer periphery at angularly spaced positions about an axis of angular movement of said core, and further including a shaft supporting said core for said angular movement, said axis being eccentric in relation to the internal lobes of said other of said structures, and wherein said means applying pressure includes means commutating fluid pressure to said opposite positions of certain ones but less than all of said rollers for each angular orientation of said core, thereby pressurizing certain ones but less than all of said rollers into said engagement at any time during angular movements of said rotor core.

4. Fluid-pressure apparatus as set forth in claim 3 wherein said commutating means commutates the higher of the fluid pressures from the inlet and outlet to said opposite positions.

5. Fluid-pressure apparatus as set forth in claim 3 further comprising valve means mounted in said housing in position to conduct flow of the fluid between said inlet and outlet in bypass relation to said spaces, means normally biasing said valve means to an open condition wherein it conducts said flow, and means for closing said valve means to block said flow and render said apparatus operative and sealed.

6. Fluid-pressure apparatus as set forth in claim 5 wherein said valve means comprises an electrical solenoid-actuated valve.

7. Fluid-pressure apparatus as set forth in claim 3 further comprising a plurality of piston-seat members fitted in radially slidable and substantially fluidtight relation within an accommodating piston chamber in said core each at a different angular position about said axis, said piston-seat members each having a seat surface mated with one of said rollers in substantially fluidtight relation therewith and permitting rotation of the associated one of said rollers in said seat surface thereof.

8. Fluid-pressure apparatus as set forth in claim 7 wherein said rollers are substantially cylindrical, wherein said seat surfaces of said piston-seat members are substantially semicylin drical concave surfaces, wherein the lobes of said other of said structures are substantially sinuous and extend substantially parallel with said rollers in direction of said axis, and wherein said rollers, core, piston-seat members and lobes of said other of said structures are of substantially the same axial length.

9. Fluid-pressure apparatus as set forth in claim 8 wherein said other of said structures is mounted for rotation in said housing in eccentric relation to said axis.

10. Fluid-pressure apparatus as set forth in claim 7 wherein said commutating means includes at least one commutating port opening in said housing in communication with the higher of the fluid pressures from the inlet and outlet, said core being disposed to close said commutating port opening except at predetermined positions where openings are disposed in said core to communicate fluid pressure from said port opening to said piston chambers and thereby force said piston members and rollers radially outwardly in relation to said core.

11. Fluid-pressure apparatus as set forth in claim 10 wherein said core openings are exposed at different angular positions about said core axis at one axial extremity of said core.

12. Fluid-pressure apparatus as set forth in claim 11 including two spaced commutation port openings in said housing, said commutation port openings and said core openings being substantially the same radial distance from said core axis.

13. Fluid-pressure apparatus as set forth in claim 12 further comprising substantially planar sealing surfaces at the axial extremities of the assembly of said rollers, core, piston-seat members and said other of said structures, wherein said rollers are substantially cylindrical, wherein said seat surfaces of said piston-seat members are substantially semicylindrical concave surfaces, wherein said lobes of said other of said structures are substantially sinuous and extend substantially parallel with said rollers in direction of said axis, wherein said other of said structures is mounted for rotation in said housing in eccentric relation to said axis, wherein said rollers, core, piston-seat members, and said other of said structures are of substantially the same axial length, and wherein said two commutating port openings are at diametrically opposite positions about said axis and extend through one of said planar sealing surfaces.

14. Fluid-pressure apparatus as set forth in claim 13 wherein said port means comprise angularly spaced openings through one of said planar sealing surfaces, said angularly spaced port openings being disposed substantially on opposite sides of the angular position of said diametrically opposite commutating port openings.

15. Fluid-pressure apparatus as set forth in claim 14 wherein one of said planar sealing surfaces appear on one side of an axially movable pressure-applying member, means applying the higher of the fluid pressures from said inlet and outlet to the opposite side of said pressure-applying member and thereby dynamically forcing said one of said surfaces against said assembly.

16. Fluid-pressure apparatus as set forth in claim 14 further comprising means for rotating said shaft and thereby causing fluid to be pumped from said inlet to said outlet, and wherein said commutating ports are in communication with said outlet port. 

1. Apparatus of the type comprising a pair of cooperating rotor structures having external and internal lobes, respectively, one of said structures being mated eccentrically within and having one less lobe than the other, the lobes of said one of said structures being formed by rollers rotatably mounted on said one of said structures at angularly displaced positions and each disposed in substantially line-contact engaging relationship with lobe surfaces of the other of said structures, and means responsive to fluid pressures applying pressure to at least certain ones of said rollers at positions substantially opposite the positions of engagements thereof with said lobe surfaces of said other of said structures, whereby said rollers are pressurized into firm line-contAct rolling engagements with said lobe surfaces of said other of said structures.
 2. Fluid-pressure apparatus comprising a fluid-tight housing having a fluid inlet and outlet, a pair of cooperating rotor structures within said housing having external and internal lobes, respectively, one of said rotor structures being mated eccentrically within and having one less lobe than the other, the lobes of said one of said structures being formed by rollers rotatably mounted on said one of said structures at angularly displaced positions and each disposed in substantially line-contact engaging relationship with lobe surfaces of the other of said structures, port means connecting said inlet and outlet with spaces between said mated structures at different spaced angular positions, and means responsive to fluid pressures applying pressures to at least certain ones of said rollers at positions substantially opposite the positions of engagements thereof with said lobe surfaces of said other of said structures, whereby said rollers are pressurized into firm line-contact rolling engagement with said lobe surfaces to effect tight sealing of said spaces.
 3. Fluid-pressure apparatus as set forth in claim 2 wherein said one of said structures includes a core on which said rollers are carried about the outer periphery at angularly spaced positions about an axis of angular movement of said core, and further including a shaft supporting said core for said angular movement, said axis being eccentric in relation to the internal lobes of said other of said structures, and wherein said means applying pressure includes means commutating fluid pressure to said opposite positions of certain ones but less than all of said rollers for each angular orientation of said core, thereby pressurizing certain ones but less than all of said rollers into said engagement at any time during angular movements of said rotor core.
 4. Fluid-pressure apparatus as set forth in claim 3 wherein said commutating means commutates the higher of the fluid pressures from the inlet and outlet to said opposite positions.
 5. Fluid-pressure apparatus as set forth in claim 3 further comprising valve means mounted in said housing in position to conduct flow of the fluid between said inlet and outlet in bypass relation to said spaces, means normally biasing said valve means to an open condition wherein it conducts said flow, and means for closing said valve means to block said flow and render said apparatus operative and sealed.
 6. Fluid-pressure apparatus as set forth in claim 5 wherein said valve means comprises an electrical solenoid-actuated valve.
 7. Fluid-pressure apparatus as set forth in claim 3 further comprising a plurality of piston-seat members fitted in radially slidable and substantially fluidtight relation within an accommodating piston chamber in said core each at a different angular position about said axis, said piston-seat members each having a seat surface mated with one of said rollers in substantially fluidtight relation therewith and permitting rotation of the associated one of said rollers in said seat surface thereof.
 8. Fluid-pressure apparatus as set forth in claim 7 wherein said rollers are substantially cylindrical, wherein said seat surfaces of said piston-seat members are substantially semicylindrical concave surfaces, wherein the lobes of said other of said structures are substantially sinuous and extend substantially parallel with said rollers in direction of said axis, and wherein said rollers, core, piston-seat members and lobes of said other of said structures are of substantially the same axial length.
 9. Fluid-pressure apparatus as set forth in claim 8 wherein said other of said structures is mounted for rotation in said housing in eccentric relation to said axis.
 10. Fluid-pressure apparatus as set forth in claim 7 wherein said commutating means includes at least one commutating port opening in said housing in communication with the higher of the fluid pressures from the Inlet and outlet, said core being disposed to close said commutating port opening except at predetermined positions where openings are disposed in said core to communicate fluid pressure from said port opening to said piston chambers and thereby force said piston members and rollers radially outwardly in relation to said core.
 11. Fluid-pressure apparatus as set forth in claim 10 wherein said core openings are exposed at different angular positions about said core axis at one axial extremity of said core.
 12. Fluid-pressure apparatus as set forth in claim 11 including two spaced commutation port openings in said housing, said commutation port openings and said core openings being substantially the same radial distance from said core axis.
 13. Fluid-pressure apparatus as set forth in claim 12 further comprising substantially planar sealing surfaces at the axial extremities of the assembly of said rollers, core, piston-seat members and said other of said structures, wherein said rollers are substantially cylindrical, wherein said seat surfaces of said piston-seat members are substantially semicylindrical concave surfaces, wherein said lobes of said other of said structures are substantially sinuous and extend substantially parallel with said rollers in direction of said axis, wherein said other of said structures is mounted for rotation in said housing in eccentric relation to said axis, wherein said rollers, core, piston-seat members, and said other of said structures are of substantially the same axial length, and wherein said two commutating port openings are at diametrically opposite positions about said axis and extend through one of said planar sealing surfaces.
 14. Fluid-pressure apparatus as set forth in claim 13 wherein said port means comprise angularly spaced openings through one of said planar sealing surfaces, said angularly spaced port openings being disposed substantially on opposite sides of the angular position of said diametrically opposite commutating port openings.
 15. Fluid-pressure apparatus as set forth in claim 14 wherein one of said planar sealing surfaces appear on one side of an axially movable pressure-applying member, means applying the higher of the fluid pressures from said inlet and outlet to the opposite side of said pressure-applying member and thereby dynamically forcing said one of said surfaces against said assembly.
 16. Fluid-pressure apparatus as set forth in claim 14 further comprising means for rotating said shaft and thereby causing fluid to be pumped from said inlet to said outlet, and wherein said commutating ports are in communication with said outlet port. 